## 2.1 Circles and Arcs

### Circle

- The set of all points in the plane that are a
**fixed distance (the radius,**from a*r*)**fixed point (the centre,**.*O*) - The angle at the centre of a circle is 360°.

### Diameter (*D*)

- A chord passing through the centre.
*D =*2*r*, twice the length of the radius.

### Circumference of a Circle

- The circumference of a circle, AKA the
**perimeter**, is given by:

c=2 \pi r

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